3.12.63-rt85-rc2 stable review patch.
If anyone has any objections, please let me know.
------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Upstream commit 47be61845c77 ("fs/dcache.c: avoid soft-lockup in
dput()") changed the condition _when_ cpu_relax() / cond_resched() was
invoked. This change was adapted in -RT into mostly the same thing
except that if cond_resched() did nothing we had to do cpu_chill() to
force the task off CPU for a tiny little bit in case the task had RT
priority and did not want to leave the CPU.
This change resulted in a performance regression (in my testcase the
build time on /dev/shm increased from 19min to 24min). The reason is
that with this change cpu_chill() was invoked even dput() made progress
(dentry_kill() returned a different dentry) instead only if we were
trying this operation on the same dentry over and over again.
This patch brings back to the old behavior back to cond_resched() &
chill if we make no progress. A little improvement is to invoke
cpu_chill() only if we are a RT task (and avoid the sleep otherwise).
Otherwise the scheduler should remove us from the CPU if we make no
progress.
Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
fs/dcache.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 50ddb10aced6..cc739409efbf 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -39,6 +39,8 @@
#include <linux/prefetch.h>
#include <linux/ratelimit.h>
#include <linux/list_lru.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
#include "internal.h"
#include "mount.h"
@@ -617,6 +619,8 @@ again:
*/
void dput(struct dentry *dentry)
{
+ struct dentry *parent;
+
if (unlikely(!dentry))
return;
@@ -645,9 +649,19 @@ repeat:
return;
kill_it:
- dentry = dentry_kill(dentry);
- if (dentry)
+ parent = dentry_kill(dentry);
+ if (parent) {
+ int r;
+
+ if (parent == dentry) {
+ /* the task with the highest priority won't schedule */
+ r = cond_resched();
+ if (!r && (rt_task(current) || dl_task(current)))
+ cpu_chill();
+ } else
+ dentry = parent;
goto repeat;
+ }
}
EXPORT_SYMBOL(dput);
--
2.8.1
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